FIG. 1 illustrates a partial cross-sectional view of a vertical-type heat treatment apparatus known in the art. The heat treatment apparatus includes a reaction chamber 1 having a wall 2, the chamber being made of a high purity material such as quartz and the like. The wall 2 is formed in a cylindrical shape which has a closed end and an open end, the open end being connected to a manifold 4. The connection between the open end of the reaction chamber wall 2 and the manifold 4 is provided with a vacuum seal, such as an O-ring 11 or the like. Most of the wall 2 is surrounded by heater 13 for heating the reaction chamber 1.
A compartment tube 3 mounts on the manifold 4, the compartment tube having a length that reaches to approximately the top of the reaction chamber 1. Also, an inlet 9 is provided in the manifold 4 for introducing a reactant gas below the compartment tube 3. An outlet 10 in the manifold 4 is provided for exhausting reaction gas above a position where the compartment tube 3 connects to the manifold.
Inside the compartment tube 3, an object supporting boat 5 supports a plurality of objects 7, such as semiconductor wafers, with a vertical space therebetween. A boat table 6 is provided for supporting the boat 5, and for loading and unloading the assembly into the reaction chamber 1. A typical treatment process for the objects 7 is to form a thin film by a chemical vapor growth, an annealing, and the like. A flange 8 is provided below the manifold 4 for shielding an opening of the manifold. An elevator mechanism (not shown) moves the flange 8 vertically within an elevator chamber (also not shown). The flange 8 can be vertically elevated by the motion of the elevator mechanism. The boat table 6 mounted on the flange 8, and the boat 5 are thus loaded into and unloaded from the reaction chamber 1. When the flange 8 contacts a shoulder formed under the manifold 4, the reaction chamber is sealed, such as with an O-ring 12, and is separated completely from the exterior environment.
The typical treatment is performed by introducing the reaction gas from the inlet 9 after placing the objects 7 in the reaction chamber 1 and forming a seal. The reaction gas goes upwardly through the inside of the compartment tube 3 past the objects 7 within the boat 5 where a predetermined reaction is accomplished. The reaction gas then passes through the opening of the upper part of the compartment tube 3 and downwardly through a space between an outer wall of the compartment tube and an inner surface of the reaction chamber wall 2. The reaction gas is then exhausted from the outlet 10 provided in the manifold 4.
In the prior art, as mentioned above, a vacuum seal member, such as an O-ring 11 and the like, is provided at the connection between the reaction chamber wall 2 and the manifold 4. Such a vacuum seal member is easily degraded causing particles in the reaction chamber to increase, and, the CVD apparatus and the quality of CVD film is thus degraded.
Moreover, the manifold 4 is typically made of stainless steel which degrades, thus producing metal molecules which spread from the manifold heated to a high temperature. The metal contaminates the objects 7, thus considerably worsening the characteristics of the processed objects.